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Unread 15-03-2007, 21:50
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Tristan Lall Tristan Lall is offline
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Re: YMTC: Redabot Scores 30 Bonus Points?

Cody has the right idea here: "supported" isn't a defined term in the manual (when referring to robots on top of each other). He quoted a standard layman's definition, which is a good starting point. But from a physics point of view, we need to ask ourselves whether supporting something means to withstand a normal force due to that thing, or if resistance to other forces (e.g. frictional forces) comes into play.

For the simple case where a robot is on top of another robot's ramp, and that ramp is on top of a toroid, the result is unambiguous: the top robot is obviously being (indirectly) borne upon the toroid. No points are scored.

For the more complex case where the top robot is on one ramp, and another ramp, independently connected, is on top of a toroid, the definition of support becomes important, as a matter of principle. Of course, given that the Q&A says that "any Robot supported by a robot supported by a Game Piece" does not earn bonus points, it seems that as far as the rules are concerned, there's still no question. No points are scored.

The real issue here is why the Q&A assumes that having Red 1, partially supported by a toroid and fully supporting Red 2 means that Red 2 is supported by that same toroid. Hypothetically, assume that Red 1's first ramp (supporting Red 2) is attached to the rest of the robot by a cable (too short to be an entanglement risk), and otherwise only supported on a series of legs, and its second ramp is mounted in some other fashion (let's say a hinge attached to the robot frame) and resting on top of a toroid. The only way that Red 2 is supported by the toroid is if the definition of supported also takes into account the internal forces within the cable. And because the cable could be slack, these aren't just tension forces; these could be the internal shear forces that resist the disintegration of the cable. That makes for a peculiar definition of support. I suspect that they just forgot to consider this case, but wrote the Q&A response in a way that inadvertently covers it. Alternatively, it could be written this way deliberately, to avoid the referees having to make a determination as to whether support exists—they just treat everything as supported.

Another case is a statically indeterminate system: Red 1's ramp that supports Red 2 also lightly pinches a toroid between the alliance station wall and the ramp. A friction force between the toroid and the ramp resists the downward motion of the ramp, as does a normal force (through the floor). If you take the toroid away, and nothing else moves, can we truly say that the ramp was not being supported by its friction force? Or do we now have friction to worry about when determining support? In actual fact, the forces on the ramp changed appreciably, and the microscopic deflections due to that frictional shear force are replaced with deflections due to the compressive normal force. On a practical level, a method of checking for this is impossible to implement. But if we aren't careful with our definition of "support", we shouldn't be surprised when someone argues that the inability of the referees to measure the state of the ramp shouldn't be an impediment to the theoretical implications of that state being taken into account when the rules are applied.

I should also note that there isn't a rule conflict here; as it stands, the rules and the Q&A are mutually consistent on this point. It's just that some of the more obscure consequences don't exactly follow from the justification provided. That doesn't make it a good ruling, but it does look like an enforceable one. As for the call, blue wins.

Last edited by Tristan Lall : 15-03-2007 at 21:57.
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